Yes, you can achieve filtration down to 1 micron with the correct fabric and surface treatment and the correct air to cloth ratio for your particular application. For wood dust, we generally recommend polyester felt with a singed finish. However, various applications require different weights of felt and surface treatments. Initially, the polyester felt material filters the dust while building a “dust cake” on the singed surface of the felt. This dust cake then does the actual filtering of all subsequent dust that is blown into the bag. When the dust cake gets too thick, the material starts to “blind” or plug up, but the singed surface of the fabric helps to prevent a thick dust cake from adhering permanently. The dust cake will break away, leaving behind a thin layer to continue the process.
The purpose of an oversized bag is to achieve the proper air to cloth ratio. Most manufacturers of single stage units include the bottom bag into their calculation for air to cloth ratio. But once the bottom bag fills up that surface area is no longer capable of filtering.
Most of the OEM bags these days are made from a woven lightweight polyester sateen which has a rating of around 30 microns and a lower air flow rate than polyester felt. The felt that comes on most OEM collectors is better than the polyester sateen, but usually has no surface treatment. AFF’s singeing treatment helps promote a dust cake buildup and release which helps the bag “clean” itself as opposed to the plain felt of the OEM bags that causes dust and woodchips to adhere.
We recommend a non-breathing collection bag to ensure that we have enough fabric area to keep the collector running efficiently even when the bottom bag is full. Our philosophy is to make the top bag the sole air relief bag and keep the bottom bag as strictly a collection bag. Our recommendation is to use a non-breathing heavy-duty canvas collector bag that can handle the abuse of constant dumping or a clear polybag that makes dumping as easy as removing the old bag and replacing with a new one.
Many of our customers have found that they didn’t need a larger dust collector for their shop, but simply more efficient dust bags. If your bags blow up more like a balloon, then you are in need of new bags that will help your collector run as efficiently as possible. Other factors that affect performance and should be considered when assessing system size are pipe length, number of bends, and number of open blast gates.
The problem is usually not the dust collector itself. To keep costs down, many manufacturers use an undersized 30 micron woven cloth (threads & holes) bag that acts like a strainer, blocking air yet allowing fine dust to escape. Switching to felt filters with fibers close together but many more paths for air to flow will increase airflow and catch the finest dust. Collector bags should be non-breathers to contain ALL dust. Larger filter bags, sized for the fan’s CFM and accounting for blockage caused by a dust cake build-up, will improve suction at your tools and minimize clean-up time.
Increasing the size of the fan motor may help, but there’s a good chance you can get better performance from your current motor. A quick check of your filter bags will tell you. If they get real hard and/or are covered with dust, they’re actually blocking free airflow and robbing vacuum. Try this first. Remove the filter bags and see if suction increases to an acceptable level. If it improves, replace the existing bags with correctly sized felt bags. To optimize performance, get 10 CFM per square foot (hobbyists can double that) for minimal back pressure and filtration down to 1 micron.
There are many factors that can cause a lack of suction at a pick up point. Some of the most common problems we run into are:
When helping a customer with their dust collection problems we usually start with the collector itself and then expand to the pickup points until we figure out the problem.
I’m trying out a new excavator next week (new to me, that is) on a small addition. However, he surprised me by saying that he doesn’t use filter fabric for the drainage pipes. He says that instead of the fines clogging the pipe, they will now just clog the fabric, so what’s the use of it? I didn’t have a good answer for him… I checked past posts, and while a few people have brought the subject up, I could find no real discussion of it.
Any thoughts???
Thanks, –Brian